One big difference between co-op and work experience is the relationship between the employer and the school. Co-op programs are usually structured more formally, and allow for more feedback between a business and a university or college. This can allow for a longer term relationship, in which employers’ feedback about student performance can be incorporated into the curriculum. Co-op programs, including accredited programs, also provide a roadmap for employers on how to build WIL into their organizations, have structured feedback and assessment, and clear guidelines for hiring. 
The reality is, however, that not all post-secondary schools have co-op or internship programs. Work Experience is a form of WIL that fills these gaps. In this case, employers trade the benefit of more flexibility (timelines; student assessment; start and end dates) with the challenge of not having as much support or a roadmap for how to implement WIL in their organization.