Wasn't Tennant scheduled/rumored to appear in one of the SJA serials, but ultimately couldn't due to a scheduling conflict? Even if he doesn't, we've still got The Brig to look forward to in a couple of weeks

I dont know the full story, just that it was rumoured he would appeared, and ive never seen the BBC officially deny it, I still hold out hope, but only a little bit.
Sarah Jane just mentions the Doctor ALOT in this one.
as for the Brig, I love how this CBBC show manages to show so much continuity with the Classic series, Sarah Janes live is not something they feel free to edit with, and use it to enhance the show. The Brig being a brilliant example of this.