[philpem]

Could also be part of the ratings scheme.

Maybe there are events triggered by a score (e.g. 3/7 is a review of skills, 6/7 is consider a promotion).

Or perhaps the manager has to justify any above-average ratings to their superiors -- meaning that "everyone gets a four" makes the wheels move slowly.

I think the most likely answer though, is that they don't feel they know you well enough (yet) to judge. One month isn't very long at all. Once you've been on a few projects, your manager will get a better feel for your skillset.

When you get to a 6- or 12-month appraisal, ask again -- but ask it differently. The question you want to ask is "Are there any things you think I could improve / any skills you'd recommend I learn or improve on?"