Writing Next

Find Writing Next: Effective Strategies to Improve Writing of Adolescents in Middle and High Schools at http://www.carnegie.org/literacy/why.html.
See page 141 for Eleven Elements of Effective Adolescent Writing Instruction.
#6 on the list is "Sentence Combining, which involves teaching students to construct more complex, sophisticated sentences." See also page 155.
See page 189- 190 for references to studies on Sentence -Combining.