The  purpose of the research  were to develop the efficient  mathematics computer  assisted instruction  in fraction  for the students in prathomsuksa 6 base on the efficiency (70/70)to compare the students  achievement  after learning with the   developed computer assisted  instruction  and  traditional  process  and  study  the students? opinion of mathematics learning activities on quadrangles using   computer assisted instruction (CAI) The sample consisted of 20 students randomly selected from 32 the students in prathomsuksa 6 of Banthungsay School.
Research instruments were the mathematics computer assisted instruction and the achievement test in fraction. The achievement test comprised 50 items possessing the degree of difficulty ranging from 0.43 -0.73,the degree of discrimination between 0.60-0.90 ,the  reliability coefficient of .82 and questionnaires on students?opinion upon mathematics learning activities on  quadrangles using   computer  assisted instruction  (CAI)
Findings of the research showed that: 1) The efficiency of the computer assisted instruction was 72.20/76.40. 2) Mathematics achievement in Fraction of students learning with the computer  assisted instruction  was statistically significantly higher than that of  students learning with traditional process at .01 level. 3)The students expressed a good opinion of mathematics learning activities on quadrangles using computer assisted instruction.
