In ARD meetings, sometimes these terms are used interchangeably. However, there’s a big difference in the purpose of these terms.
Accommodations affect how a student learns material. Accommodations help the student meet the same expectations as their peers. For example, a student with ADHD can have their difficulties with processing (how quickly they are able to perform tasks) accommodated by providing them with additional time to complete assignments.
Modifications affect what material a student learns. Modifications are utilized for students who are functioning below the expectations of peers. For example, a 7th grade student who is reading at a 3rd grade level can have their reading assignments modified by being provided assignments that are equivalent to a 3rd grade reading level and/or are shorter in length.