The OAT and DAT are sibling exams -- both administered by the American Dental Association's Department of Testing Services, both computer-based at Prometric testing centers -- but they're built for different professional paths, and the differences matter if you're deciding between optometry and dentistry, or studying for both.
Section structure
The OAT has four sections: Survey of the Natural Sciences, Reading Comprehension, Physics, and Quantitative Reasoning -- all covered in full by this site's practice bank, since the OAT has no excluded section. The DAT also has four sections, but swaps the OAT's Physics section for the Perceptual Ability Test, a spatial/3D-rotation image-based section this site's text-based question bank doesn't cover. This is the single biggest structural difference: the OAT has no spatial/image-based content at all, and the DAT has no Physics content at all.
Related: What to Expect on the OAT: Format, Scoring, and How to Prepare
Survey of the Natural Sciences overlap
Here's the genuinely useful fact if you're studying for both: the Survey of the Natural Sciences section covers essentially the same topic breadth on both exams -- the same Biology, General Chemistry, and Organic Chemistry topic areas, in the same 40/30/30 question split. Strong prep in this section transfers directly between the two exams.
Quantitative Reasoning differences
Both exams provide a basic four-function calculator for Quantitative Reasoning, and the topic areas and format are essentially identical between the two. Prep here transfers well between the two exams, same as Survey of the Natural Sciences.
Scoring scales
This is a common point of confusion: the OAT is scored 200-400 per section, while the DAT is scored 200-600 per section (as of March 1, 2025) -- a genuinely different scale, despite sharing an administering body. Don't assume a "good OAT score" and a "good DAT score" look numerically similar; check score expectations for optometry schools separately from dental schools.
Which exam do you actually need?
This isn't really a choice -- it's determined by which professional path you're pursuing. Optometry school admissions require the OAT; dental school admissions require the DAT. If you're genuinely exploring both paths and haven't decided, note that the Physics content on the OAT and the Perceptual Ability Test on the DAT each require dedicated prep time the other exam simply doesn't test -- factor that into your decision if timing or workload is a real constraint.