The purposes of this research were to synthesize thesis concerning factors onCAI lesson in Thailand since B.E. 2528 - 2540 in order to obtain clear conclusion onthe variable concerning with the CAI lesson factors and to study the differencesamong the CAI lesson factors which effect upon learning achievement. The data forthis synthesis consisted of 112 research reports. One hundred researches wereselected for calculating the effect size by studying in the 6 factors

learnercharacteristics, cueing, pacing, presentation format, methodology and activity, andfeedback. These research factors had 45 mainvariables and 134 subvariables. The datawere analyzed by descriptive statistic, the unbiased estimators of effect size,t-test and the multiple regression analysis. The factors on CAI lesson were treatedas an independent variable and the effect size as a dependent variable. The results indicated as follows: 1. For all 112 theses, a large number of theses were conducted at theChulalongkorn university and Srinakarintaravisoj prasanmitra university, studied insecondary education, concentrated on mathematics subject and concerning factor inlearner characteristics. 2. The factors which effect on the instructional effectiveness with asignificant at 0.05 level according to mean of the effect size and the standardregression coefficience were the learning aptitude, the language aptitude, the levelof basic knowledge, the boy - girl matchedpair learning method, the drill andpractice, cueing, advanced organizer formats and lesson presentation. 3. Regression analysis of 6 predictors indicated that the predictors were ableto explain 18.60% of effect size. The stepwise method showed that the 3 factors,learner characteristics, methodology and activity, and feedback effect on theinstructional effectiveness at 0.05.