The expansions are needed to provide additional places in response to an “unprecedented birth rate increase”.
Works will create 210 new places at Christ Church CE Primary and a further 210 at Rowley Hall Primary as part of a borough-wide £7 million programme to make 630 extra places available.
Nine new classrooms, a nursery, small hall, studio and kitchen will be created at Rowley hall, while an extension at Christ Church will include a reception classroom, eight general teaching bases and a new main entrance.
Sandwell Council's cabinet member for children and families Councillor Bob Badham described the extensions as proving “state-of-the-art facilities”.
He said: "It is important that we continue to provide quality places in areas of demand and this work will do just that.
"We have already provided over 300 new reception places over the last two years across Sandwell and this programme of expansion is set to continue as more young people choose to live and raise their families here."
The Rowley Hall extension at Rowley Hall is to be constructed using a super insulated panel system and the work at both school is being carried out through the council’s Local Education Partnership with Sandwell Futures Ltd.
Works to address further school expansions are to shortly start on other schools including Brandhall Primary, Oldbury, and Grace Mary Primary, Old Hill.