The purposes of this research were to 1) develop the screening and intervention system for students at risk in misbehavior using RTII MODEL and 2) study on the effects of implementing screening and intervention system for students at risk in misbehavior using RTII MODEL. The researcg design was mixed methods with two phases of the research were conducted. The first phase was developing screening and intervention system using RTII MODEL. The second phase was to study on the effects of implementing screening and intervention system for students at risk in misbehavior using RTII MODEL. The target group consisted of principal, counselors, and Mathayomsuksa 1-3 Students by purposively selected. The research instruments were Strength Difficulties Questionnaire, Three Tiers instruction and intervention lesson plans, and satisfaction questionnaires. The statistics used in this research were percentage, mean, percentage, standard deviation, content analysis, and descriptive conclusion. The research results revealed that the screening and intervention system for students at risk in misbehavior using RTII MODEL consisted of building team of counselors for using student screening and intervention system using RTII MODEL; teaching ordinary counseling course; 1st screening, tier-1 intervention; 2nd screening for students at risk from 1st screening; tier-2 intervention for students who were identified as at risk group and tier-3 intervention for students who were identified as problem group, 2) the effects of implementing a screening and intervention system for students at risk in misbehavior using RTII MODEL found that 1) number of students: after the second and third screenings, no students were at risk in misbehavior at every level. But there were still 1 student with behavioral problems at all level. 2) behavioral progress of students at risk in misbehavior had a high level of behavioral progress from level 1 to level 2 and level 3, but some behavioral progress remained constant at level 2 and there was 1 grade 9 student had a stable behavioral progress at level 1 in cherishing Thai-ness. and (3) teachers were satified with sorting nad support system for at risk students at a high level and students were satified with the screening and intervention system for students at risk in misbehavior using RTII MODEL at a high level.