Once built, the contractor will deliver facilities management services at Rainford worth an estimated £15m over a 25-year period.
E4L’s partner Agilisys will be providing ICT equipment and related managed services.
At De La Salle, which will have places for 1,215 pupils from ages 11 to 16, around half the buildings will be new while the remainder will undergo major refurbishment.
Two thirds of the Rainford school project will consist of newly-built facilities ultimately providing places for 1,650 pupils from ages 11 to 18.
E4L and St Helens Council will form the St Helens Local Education Partnership (LEP), a strategic partnership opening the opportunity to put forward proposals to work with the council on future developments over a 10-year period.
The contractor and its consortium partner Barclays European Infrastructure Fund will each invest £1.8m, while the Co-operative Bank will provide £33m funding for the projects.
Interserve has just signed off three other schools projects worth £42m in Leeds, Nottinghamshire and Coventry and is currently engaged in extensive development work on a number of schools in Sandwell, West Midlands, including Sandwell College, which will open in 2011.