Projects need to be designed to work on lots of skills, because they usually take so much time to complete. Inevitably, these activities would have to integrate skills needed on a standardized test. It also takes lots of time for the teachers to individually assess the students. In addition educators must find time to get together and have a common standard of how all teachers will Asses students in their age bracket. Money is also a big concern.
Schools have to have the technological resources and project or lab materials for students to use.
While, most schools may have these things, they may not have enough resources for lots of children to use at the same time. For the most part performance-based assessment has far more advantages then disadvantages. Traditional testing has their place in the academic world, but should be viewed as only an option, not a standard. Like portfolios authentic assessment is sometimes thought of as a sublet of performance based assessment. Even though it as similar attributes, it is distinct enough to be discussed by itself.