The three contracts – worth £28m in total – are for Cromwell Community College in Chatteris, Sir Harry Smith Community College in Whittlesey and Meadowgate Special School in Wisbech.
Kier Eastern will provide new accommodation and facilities at all three schools, as well as refurbishing much of the existing accommodation.
Work starts on site this month, with completion for last of the three schools due by August 2013.
Cambridgeshire County Council BSF programme director Alan Kippax said: “These contracts have been signed six months earlier than originally planned. This has been achieved as a result of a huge amount of work by the three schools, the county council, our private sector partners and Partnerships for Schools, who have all worked extremely well together to ensure that these exciting developments go ahead.”
Kier Eastern managing director Graham Howe added: “This is a tremendous achievement by all, and a tribute to the hard work, co-operation, support and positive approach by everyone involved. I know the staff and pupils are looking forward to their new facilities, and we look forward to working with them - we can’t wait to get started.”