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Digi-Block, gr. 2-4. Starter kit contains 300 blocks, 30 tens holders, 3 hundreds holders, 1 thousands holder, three-place digi-counter, desktop place mat, 0-9 digi-flip card books, 1 array mat, 1 teacher's guide, $119.98. Delta Education, 125 Walnut St., Watertown, MA 02472, (617) 926-9300.

The Digi-Block product is a manipulative set designed to teach students about the base-ten nature of our number system. The attribute that distinguishes it from other base-ten manipulatives is the way that the blocks fit in a container that looks like a larger version of the smaller block yet is easily unpacked into its unit equivalents. For example, ten unit blocks pack inside a ten-block, which then looks exactly like a unit block, but larger.

The set comes in three levels--grades K-l, 1-2, and 2-4. Each level includes unit digi-blocks; holders for tens, hundreds, and thousands; place-value mats; number cards; number lines; and a packing template counter. The counter shows when it is time to pack together blocks to make a larger bundle. …