Sweet Spot (109 Street) has higher quality junior racquets as described below.
These are graphite racquets that are just shorter (and smaller gripped) versions of the adult 27″ size. As you shift to a green dot level, you might want to consider these.
Semi Solid Racquets
These are a hybrid of graphite and aluminum. You can actually get these at the 23″ length (25/26″ as well.) They are a step up from the aluminum-only introductory racquets. You want at least this quality as you shift to green dot ball tennis, as the cheaper (strictly aluminum) racquets can be somewhat flimsy.