My children (and some of my students) use the very basic and highly illustrated, large print School Speciality Publishing materials from the "American Education Publishing" series, e.g.
"The Complete Book of English and Language Arts" grades 3-4 (Sam's Club, $5.82),
"Total Reading" grade 4,
"The Complete Book of Grammar and Punctuation" grades 3-4.
Scholastics and Viking Press also offer good books.
Stenson House has a very inspiring website with lots of book reviews, interviews, links and excellent articles on cutting edge teaching techniques and aids as well as great books, some of which you can preview online gratis-- and of course you can always check out many homeschooling websites with lots of useful and excellently researched and collated free instructional materials, easy to download and print. In fact, even ESL sites have lots of free instructional materials you can share with your children and which are geared to children of all ages.
You might find some of these tests and articles on differentiated learning (from the MIS website) interesting:
http://www.frsd.k12.nj.us/rfmslibrarylab/d...instruction.htm