The study investigated the relationship between mathematics achievement, cognitive and motor skills, and general intellectual ability among seventy 10-12 years old students with mild intellectual disability (MID) attending regular school (n = 30) and special school (n = 40). The purpose of the study was to identify the critical deficits teachers need to consider when teaching mathematics at the secondary school level. The students attending regular schools had significantly higher fluid intelligence scores (p = 0.036), but we found no difference in the total score of the math achievement test. Special school students were more eager to use assistance and aids when solving math problems (p = 0.040). The study indicated significant associations between basic mathematical skills, verbal and visuospatial processing, and motor skills. Thus, it is essential to compensate for the delay of students' cognitive development to improve their basic mathematical skills and, in general, mathematical performance. The educational placement affects the willingness or ability to seek academic help when solving mathematical problems.