Complex sentence: In the 1960s and 1970s the company's Key Words Reading Scheme (launched in 1964) was heavily used by British primary schools, using a reduced vocabulary to help children learn to read.
Split into simpler sentences: In the 1960s and 1970s the company's Key Words Reading Scheme (launched in 1964) was heavily used by British primary schools. It used a reduced vocabulary to help children learn to read.