Improvements relating to teaching methods and aids.
A teaching aid comprising a base having a plurality of spaced parallel ridges which define channels between adjacent ridges, the ridges having an inverted u section and the channel having a corresponding u section and the ridges having sides which bulge outwardly into the adjacent channels; and a plurality of pieces adapted to engage releasably ridges and to be retained on the ridges or in the channels by the bulges. Preferably the pieces clip resiliently onto the ridges. CLAIMS 1. A teaching aid comprising a base having a plurality of spaced parallel ridges which define channels between adjacent ridges, the ridges having an inverted U section and the channels having a corresponding U section and the ridges having sides which bulge outwardly into the adjacent channels; and a plurality of pieces adapted to engage releasably ridges or channels and to be retained on the ridges or in the channels by the bulges. 2. An aid according to claim 1 in whcih the pieces clip resiliently onto the ridges or into the channels. 3. An aid according to claim 1 or claim 2 in which the pieces which are adapted to engage ridges are slidable along the ridges. 4. An aid according to any one of claims 1 to 3 in which the channels have spaced holes in their bases and tne pieces which are adapted to engage channels have projections adapted to fit into the holes to prevent those pieces from sliding in the channels, with spigot-like projections on their upper surfaces adapted to engage edges of indicia-carrying cards, the cards being retained between the spigot-like projections of adjacent pieces. 5. An aid according to any one of claims 1 to 4 in which at least some of the pieces carry indicia on their upper surfaces. 6. An aid according to claim 4 or claim 5 in which the indicia are letters or numerals. 7. An aid according to claim 4 or claim 5 in which the indicia are pictures or parts of pictures. 8. An aid according to any one of claims 1 to 7 in which the base has an engaging formation on one edge and a complementary engaging formation on an opposite edge so that two or more bases can be attached to one another.