I completely agree with the practice of giving them a group exercise to be completed ON-SITE to assess how they work with the team and collaborate. But I want to note that start ups should generally avoid assigning at-home (i.e. HOMEWORK) assignments, for seasoned designers and developers.
When it comes to assessing individual skills, the first thing that should be considered is the context of the industry that your candidate’s role belongs to and you should ask for industry standard application materials, such as portfolio in the case of designers. From there only ask for what needs to fill the gaps. You should not just think about what you need, but also about the context of this person’s role and what is appropriate for their industry and role.
I have seen far too many startups ask (me personally and other seasoned designers) to redesign their home page as a homework assignment. LOL. What’s the problem with this exactly? I wrote an article about it here: https://blog.prototypr.io/interviewing-designers-for-gods-sake-don-t-give-them-homework-8b0bd271de0b
