The problem under investigation was to find out whether achievement through Mastery Learning (ML) and Direct Instruction (DI) was dependent on the aptitude of student-teachers in the graduate teacher training programme or not. The objectives of the study were to ascertain the aptitude of student- teachers before teaching them through Mastery Learning and Direct Instruction, to compare the high aptitude student-teachers in their academic achievement through Mastery Learning and Direct Instruction. Further objectives were to compare the low aptitude student-teachers in their academic achievement through Mastery Learning and Direct Instruction. Moreover, to compare the academic achievement of student-teachers having high and low aptitude taught through Direct Instruction and to compare the academic achievement of Mastery Learning group and Direct Instruction group of student—teachers. It was an experimental study. The population of the study consisted of student-teachers enrolled in B. Ed. programme in Federal College of Education, Islamabad. The sample comprised of 116 student- teachers of B. Ed. class of Federal College of Education. Research findings revealed that the student- teachers having high and low aptitude differed in their achievement after teaching them through Mastery Learning and Direct Instruction respectively, the difference being in favour of those taught through Mastery Learning. The student-teachers with high and low aptitude did not differ in their achievement when exposed to teaching through Mastery Learning. The student-teachers with high and low aptitude however differed in their achievement when exposed to teaching through Direct Instruction, the difference being in favour of student-teachers having high aptitude. Mastery Learning was found to be equally effective for student-teachers having high and low aptitude for teaching, whereas Direct Instruction was found to be effective for student-teachers having high aptitude. The major recommendations of the study were: Keeping in view the significance of aptitude, the enrollment selection criteria may suitably be modified. The text, lesson plans, co-curricular activities and behaviour of teacher may have a positive influence on aptitude. Therefore, these aspects may be improved and further research may be conducted on these aspects. Instructional material should be developed based on these two models of teaching for different subjects at different grade levels. These two models of teaching should be tested on under-achievers and over-achievers in terms of their achievement.