I've conducted many interviews hiring for a growing tech company pulling from a large pool of new hires (4 major universities) as well as a metro with software pedigree.

With younger developers (or fresh grads) its about their propensity to learn rather than anything they've learned to do before, chances of a fresh grad having previously worked on something that would move the needle in 3 months are slim.

Reviewing their profile: prior internships and/or limited work experience offer are openers for how they might operate in a workplace, how they crack open problems and how well they handle the 'I don't know how to do this scenarios' (of which there will be many).

I refuse to whiteboard, so for the technical aspect, probe the keywords mentioned in order to ascertain what they were really accountable for and what is simply fluff, paying close attention to how they articulate their work and its impact at the company.

The rewards of a well-mentored junior developer are tremendous, though very time consuming at the onset, so make sure whomever you pick is a good fit that you'll be happy to work with.