Scholastic, publisher of educational materials for children, signed two new leases in New York's landmark Soho district. The 128,000 square feet of additional office spaces are equidistant from its 220,000 square foot headquarters at 555 Broadway, renovated in 1992. Among the amenities enjoyed by Scholastic staff in their plush surroundings, rumor has it, are personal trainers and a private health club. This is another factor for artists to consider when the next Scholastic work-for-hire contract is offered.