Hidamari Sketch will be returning for a
fourth season (per the official website), and as with prevous seasons a two-episode OVA special will be released later this year (in November) as a precursor to the new series.
Very much looking forwarding to this sequel, though I wonder if we are beginning to approach the end of the franchise (with the manga-ka just having announced a new project, and part of the original cast getting ever-closer to graduation). That said, another famous show in this basic genre has shown that there is still life after graduation, so I guess we'll see...