The Montreal experimental intervention for the prevention of psychosocial maladjustment.

Last registered on April 28, 2022


Trial Information

General Information

The Montreal experimental intervention for the prevention of psychosocial maladjustment.
Initial registration date
April 28, 2022

Initial registration date is when the trial was registered.

It corresponds to when the registration was submitted to the Registry to be reviewed for publication.

First published
April 28, 2022, 6:22 PM EDT

First published corresponds to when the trial was first made public on the Registry after being reviewed.



Primary Investigator

University of Montreal

Other Primary Investigator(s)

PI Affiliation
University of Montreal
PI Affiliation
University of Montreal

Additional Trial Information

Start date
End date
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
The 172 boys who participated in this study were a subsample of the Montreal Longitudinal and Experimental Study. In the spring of 1984, 1037 boys attending the last year of kindergarten (mean age: 6.1 years) were recruited from schools in low socioeconomic neighbourhoods of Montreal (Quebec, Canada). Gender (boys), ethnicity (White) and socioeconomic status were homogeneous as a result of the selection procedure. This study was approved by the University of Montreal Institutional Review Board, with participation in the study requiring both parental consent and child assent. From the original sample, those who received scores above the seventieth percentile on the teacher-rated disruptiveness scale (n = 250) of the Pre-school Behavior Questionnaire (PBQ) in kindergarten were classified as disruptive and designated as at-risk for conduct disorder. These boys were then randomly assigned according to a 1:1:2 randomisation scheme to one of three groups (intervention group, n= 69; no-treatment control group, n= 60; and intensive observation group, n = 121) by drawing the names from a box until the necessary numbers were obtained. Of these, 23, 18 and 37 parents from each of these groups, respectively, refused to take any further part in the study. Thus, of the 172 participants included for analysis in the current study, 46 boys and their parents took part in the intervention, 42 were assigned as controls and 84 were assigned to an intensive observation group. Boys included in analyses did not differ significantly from those who refused to participate on any of the variables implemented in this study. The intervention was implemented over 2 school years, from September 1985 to June 1987, when boys were 7–9 years of age. The first component of the intervention, social and problem-solving skills training, aimed to promote healthy peer relations. It also aimed to promote self-control and consequently reduce impulsivity and antisocial behaviour. Boys took part in training sessions at their school in small groups of four to seven children. These groups of children generally had a ratio of three to four prosocial children to one disruptive child, with a ratio of five to two in groups of seven. The sessions were conducted by four trained professionals (one psychologist, one social worker and two psychoeducators), lasted about 45 minutes each, and included verbal instructions, positive reinforcement, behaviour modelling and rehearsal. The professionals who delivered the training sessions for the boys also offered to meet twice with each teacher to monitor the child’s progress in the classroom and help the teacher set up reinforcement contingencies to support practice of the learnt skills in the classroom. However, this was implemented in only half of the classrooms with a target child because half of the teachers refused to participate in this part of the programme. The second component, training sessions for parents, was based on the Oregon Social Learning Center Model. Those sessions were conducted at the parents’ homes by a different professional from the one who worked with the children. It included teaching parents to recognise problematic and appropriate behaviours of their boys, to set clear objectives for them and reinforce appropriate behaviours. Parents were also encouraged to supervise their children’s schoolwork and behaviour outside the home. Detailed longitudinal data from these cohorts was collected on the boys’ socio-emotional development during childhood and adolescence and later adult outcomes. In partnership with Statistics Canada, we matched this longitudinal data to data from tax returns from ages 20-37 years.

Registration Citation

COTE, SYLVANA, Richard Tremblay and Frank Vitaro. 2022. "The Montreal experimental intervention for the prevention of psychosocial maladjustment.." AEA RCT Registry. April 28.
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Experimental Details


The Montreal Longitudinal and Experimental Study (MLES) began in 1984. The original aim was to study the development of antisocial behavior from kindergarten to high school with a specific focus on the role of parent-child interactions. To that purpose we assessed all the kindergarten boys in 53 schools of low socioeconomic areas in Montreal, to identify those who were most disruptive, and to intensively study the parent-child social interactions of a subset of them until high school.
In the spring of 1984, the kindergarten teachers of each of the 53 schools in the low socioeconomic areas of Montreal were asked to rate the behavior of each of their male students. Teachers typically had a morning and an afternoon group, each consisting of approximately 8 boys and 8 girls. Ratings were returned by 87% of the teachers, and 1,161 boys were rated. The next step involved identifying those who were the most disruptive. First, to control for cultural effects, we included in the longitudinal study only the boys with biological parents who were born in Canada and whose mother tongue was French (n = 1,038) and who were not older than 81 months when they finished their kindergarten year. After applying these criteria and eliminating families who refused to participate further in the study (n = 1), 1,037 boys remained. We then used 13 items of the Preschool Behavior Questionnaire (Tremblay, Desmarais-Gervais, Gagnon, & Charlebois, 1987; Tremblay et al., 1991) in order to identify the most disruptive boys: Bullies; kicks, bites, hits; fights; disobedient; blames others; irritable; destroys things; restless; inconsiderate; tells lies; squirmy; doesn’t share; not liked.
A sub-sample of disruptive boys was created by selecting those above the 70th percentile of the disruptive behavior scale from teacher ratings. Three groups of disruptive kindergarten boys were randomly created (total N=250): An intensive longitudinal observation group (Group A), an experimental intervention group (group B) and a third group of subjects which would be assessed yearly and would thus serve as a control group (Group C) for the intervention, as well as a control group for the possible effects of the intensive longitudinal observations of group A. From this perspective Group A was also an attention-control group for the experimental group (Group B).
The financial resources for this large-scale data collection became available in time to assess all the boys when the majority of them were finishing Grade 4, and turning ten years of age.
When in kindergarten, the majority of the boys lived with both their biological parents (67%), but one out of four (24%) was living alone with his mother, and 5% were living with their mothers and a man who was not the boy's father; the rest (4%) were living in other family arrangements (e.g., with grand-parents, with father and stepmother). Parents' mean age at the birth of their son was 25.4 (SD = 4.8) for mothers, and 28.4 (SD = 5.6) for fathers. This varied from 15 to 45 years for mothers, and from 16 to 56 years for fathers. The mean number of school years completed by the mothers was 10.5 (SD = 2.8), and 10.7 (SD = 3.2) for fathers. The majority of the parents were unskilled workers. The mean score on the Canadian socioeconomic index for occupations (Blishen, Carroll, & Moore, 1987) was 38.15 for mothers and 39.19 for fathers. This index ranges from 17.81 for the lowest status to 101.74 for the highest status, with a mean of 42.74 (SD = 13.28). The mean and median family income when the boys were age 10 years (1988) was between $25,000 and $30,000 (Canadian dollars; $19,000 to $23,000 in US dollars) compared with a median income of $44,000 (Canadian dollars) for couples with children in Canada in 1987 (Mitchell, 1991).
The main instruments used in the MLES to assess behavior problems are mother and teacher ratings and self-reported delinquency. Behavior ratings were also obtained annually from mothers, and from classroom peers at ages 10, 11 and 12. A structured psychiatric interview was conducted with the boys and their mothers when the boys were 15 years of age. Annual questionnaires completed by mothers provided information on family background, life events, parenting behavior, domestic relationships, and social support. Annual interviews with the boys provided information on a variety of dimensions including personality, life events, perceptions of parenting, domestic relationships, friendships, attitudes toward school and the law, sleep substance use and leisure activities. Direct observations of social interactions were made at school, at home and in laboratory situations with sub-samples between ages 7 and 15. Psychophysiological and as different biological assessments, were also made on sub-samples between age 7 and 20. Involvement in criminal activities and high school dropout status were obtained from official records by the end of adolescence and again during early adulthood. Finally, information about employment and marital status, income and social welfare receipts were obtained through Statistics Canada from ages 20 through age 37.
Teachers and mothers rated the boys' behavior in the spring, from age 6, at the end of the kindergarten year, to age 15. The six scales derived from teacher and mother ratings were: Physical aggression (fights with other children; kicks, bites, or hits other children; bullies or intimidates other children); Opposition (doesn't share materials; irritable; disobedient; blames others; inconsiderate); Covert conduct problems (destroys property, lies, steals, truants), Anxiety (tends to be fearful or afraid of new things or new situations; cries easily; appears miserable, unhappy, fearful, or distressed); Inattention (has poor concentration or short attention span; inattentive); Hyperactivity (restless, runs about or jumps up and down, does not keep still; squirmy, fidgety); and Prosocial behavior (comforts upset child; helps sick child; helps hurt child; praises other; helps with task difficulty; helps clear up mess; shows sympathy; invites bystander; stops quarrels; helps pick up objects). Teachers and mothers also reported on the children’s school performance using a rating scale.
Self-reported delinquency was assessed every year from ages 10 to 17 and around age 20. The boys were seen in small groups at their schools between March and May; they answered 27 self-reported delinquency items which were distributed in a questionnaire pertaining to school, family, friends, and leisure activities. The items were: steal from school; steal from store; steal from home; keep object worth less than $10; steal bicycle; sell stolen goods; keep object worth between $10 and $100; steal objects worth more than $100; breaking and entering; enter without paying; trespassing; take drugs; take alcohol; get drunk; destroy school material; destroy other material; vandalism at school; destroy objects at home; vandalize car; set a fire; strong-arm; gang fights; use weapon in a fight; fist fight; beat up someone; carry a weapon; throw objects at persons. The responses to all 27 items ranged from 1 (never) to 4 (very often).
The Intervention included two major components (a parent training program based on techniques developed at the Oregon Social Learning Center and a classroom-based social skills program for the children). In brief, the parent training component involved: (1) giving parents a reading program; (2) training parents to monitor their children’s behavior; (3) training parents to give positive reinforcement for prosocial behavior; (4) training parents to manage family crises; (5) use of non-abusive punishments for the child’s behavior problems; and (6) helping parents to generalize what they have learned. The parent training component was supplemented by eliciting cooperation from the teacher. Work with parents and teachers was carried out by two university-trained child-care workers, one psychologist, and one social worker, all working full-time. Each of these professionals had a caseload of 12 families. The team was coordinated by a fifth professional who worked on the project half-time. Work with the parents was planned to last for 2 school years with one session every 2 weeks. The professionals were, however, free to decide that a given family needed more or fewer sessions at any given time. The maximum number of sessions given to any family was 46 and the mean number of sessions over the 2 years was 17.4, counting families that refused to continue.
For the school based social skills training component of our interventions, two types of training were given to the disruptive boys within a small group of prosocial peers in school. During the first year a prosocial skills program was devised based on other programs (Cartledge & Milburn, 1980; Michelson, Sugai, Wood, & Kazdin, 1983; Schneider & Byrne, 1987). Nine sessions were given on themes such as “How to make contact,” “How to help,” “How to ask ‘why’,” and “How to invite someone in a group.” Coaching, peer modeling, role playing, and reinforcement contingencies were used during these sessions. During the second year the program aimed at self-control. Using material from previous studies (Camp, Blom, Hebert, & Van Doorminck, 1977; Goldstein, Sprafkin, Gershaw, & Klein, 1980; Kettlewell & Kausch, 1983; Meichenbaum, 1977), 10 sessions were developed on themes such as “Look and listen,” “Following rules,” ‘What to do when I am angry,” “What to do when they do not want me to play with them,” and “How to react to teasing.” Coaching, peer modeling, self-instructions, behavior rehearsal, and reinforcement contingencies were also used during these sessions. This component too was offered by the professionals who provided parental training, although different workers assisted the parents and the child.
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
Children’s behavior problems and academic performance from ages 9 through 12
Primary Outcomes (explanation)
Behavior problems (i.e., aggression, opposition, hyperactivity, inattention) were rated yearly by parents, teachers, peers, and independent observers; academic performance and repeating a class was measured through teacher and mother reports

Secondary Outcomes

Secondary Outcomes (end points)
delinquent behavior, substance use, school dropout throughout adolescence; criminal behavior, unemployment/income/marital status/social welfare receipts through middle-adulthood
Secondary Outcomes (explanation)
delinquency (violence, vandalism, theft) and substance use (marijuana, alcohol abuse, other drugs) was self-reported yearly by participants; school dropout and criminal behavior were assessed through official records during early adulthood; unemployment/earnings/social welfare receipts were measured through government administrative data

Experimental Design

Experimental Design
participants (250 kindergarten aggressive-disruptive boys) were randomly assigned to an intervention group (n=69), an observation-attention group or a no contact control group. Because no differences were found on any outcome between the last two groups, they were collapsed into a single control group for later analyses (n=181).
Experimental Design Details
Randomization Method
Coin flip
Randomization Unit
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
Sample size: planned number of observations
Sample size (or number of clusters) by treatment arms
intervention group (n=69), control group (n=181)
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
using a one-tailed 2-sample t-test with a sample size of 250 participants (69 vs 181), a minimal projected power of .80, and a p-value of .05, we can detect a minimum effect size of .35 (considered moderate according to Cohen’s criteria)
Supporting Documents and Materials

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Institutional Review Boards (IRBs)

IRB Name
University of Montreal
IRB Approval Date
IRB Approval Number


Post Trial Information

Study Withdrawal

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Is the intervention completed?
Intervention Completion Date
May 30, 1987, 12:00 +00:00
Data Collection Complete
Data Publication

Data Publication

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Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Tremblay et al. (1995): Disruptive kindergarten boys from inner-city low socioeconomic neighborhood schools were randomly allocated to a preventive intervention and control condition. The 2-year prevention program included a home-based parent training component and a school-based social skills training component. Participants were followed up to mid-adolescence. Results indicated that a significantly greater percentage of treated boys remained in an age-appropriate regular classroom up to the end of elementary school and that the treated boys reported significantly less delinquent behaviors at yearly assessments from 10 to 15 years old, compared with controls. The preventive intervention appeared to have a significant long-term impact on the social development of the disruptive kindergarten boys. Earlier and more intensive intervention may be necessary for some cases, whereas for all disruptive boys, booster sessions between 12 and 15 years of age are recommended.
Tremblay, R. E., Kurtz, L., Mâsse, L. C., Vitaro, F., & Pihl, R. O. (1995). A bimodal preventive intervention for disruptive kindergarten boys: Its impact through mid-adolescence. Journal of Consulting and Clinical Psychology, 63, 560-568.
Boisjoli et al. (2007): Background Many intervention programmes have attempted to reduce disruptive behaviour problems during early childhood to prevent maladjustment during adolescence and adulthood. Aims To assess the long-term impact and clinical significance of a 2-year multicomponent preventive intervention on criminal behaviour and academic achievement, using intention-to-treat analyses. Method Targeted disruptive–aggressive boys considered to be at risk of later criminality and low school achievement (n=250), identified from a community sample, were randomly allocated to an intervention or a control group. The rest of the sample served as the low-risk group. The intervention was multimodal and aimed at boys, parents and teachers. Official data measured both outcomes. Results Significantly more boys in the intervention group (13%; P<0.05) completed high-school graduation and generally fewer (11%; P=0.06) had a criminal record compared with those allocated to the control group. Conclusions The results suggest that early preventive intervention for those at high risk of antisocial behaviour is likely to benefit both the individuals concerned and society.
Boisjoli, R., Vitaro, F., Lacourse, E., Barker, E. D., & Tremblay, R. E. (2007). Impact and clinical significance of a preventive intervention for disruptive boys: A 15-year follow-up. British Journal of Psychiatry, 191, 415-419.

Reports & Other Materials