Yes, it is part of the Hans-Litten-Schule. The Southern building, marked as house nr. 26-28 is the "Altbau" or old building, built in 1908 while the Northern building was built in 1978. HistoMapBerlin has a house nr. 25-27 for this new building and 28 for the old one, but I am not sure if this is accurate. The school itself has 26-28 as the adress of its secretariat. There was a precursor building at the site where the new building of 1978 stands and which had the nr. 25. But maybe it's best to leave this house without an own house nr. as it may not have e.g. an own letter box or a sign with a number "25" or "25-27" on it.