There's a filming report from Series 5, episodes 3 and 4, of The Sarah Jane Adventures (yes you heard that right, they are filming series 5 already) over at Life, Doctor Who and Combom from a Ryan Ellis.
Ellis does a really great job at reporting what he sees. He says (read after the cut) :
Episodes 3 & 4 of Series 5 were written by Russell T Davies (according to 1st A.D), they are a story that involves something to do with the homeless, and Clyde has been cursed, apparently. (pretty sure that's what I heard). This curse has caused some weird things to happen. One of them, filmed yesterday, involved fish falling from the sky and landing in the school. For the filming they used five live fish and this scene involved Sarah Jane, Haresh Chandra and a new character running from one classroom, as Rani and Clyde run from another direction. I was in the middle of the action, and had a lovely chat with the cast between takes.
Ellis also reports that the departing character of Luke (Tommy Knight) is being replaced by a short blond girl of about 12 years old, and that there will also be a CGI fish thingy in that episode.
Please go over here to read the full report.
I'm quite surprised that they are filming series 4 and 5 together but someone has suggested it's because the actors are getting older. Could this also mean that the The Sarah Jane Adventures may end with Series 5? Nothing has been announced concerning the end of the series, yet. Time will tell.