Sometimes. Aba is one behavioral therapy shown to be effective in helping with asd. There are newer, more developmentally based therapies also showing promise, such as play project (floortime), son rise and rdi - relationship development intervention. The key factor as a parent is to research the various approaches and determine which seems to best fit your child. And don't be afraid to change, if needed.
For some. Aba is well studied and can be effective when the major problem is autism-related resistance to interacting with others, making education nearly impossible. It is not needed for everyone and does not help specifically with mental retardation. It often is touted as a "cure, " but a relatively small number of children become symptom free even with prolonged, intense aba.
ABA is the only. evidence-based treatment at this time. Research shows that ABA has to be intensive, at least 25-40 hrs./wk., repetitive & aimed at the child's developmental level. I work with Erik Lovaas, Dr. Ivar Lovaas' son. He can ignore screaming for > 2 hrs., shape adaptive behaviors & write up precise outcome measures. Prognosis depends on degree of Autism, level of cognition & early response to therapy.