Vol. 13 Num. 3 (1993) Ronald Narode When mathematicians and mathematics teachers come together2 Richard Pallascio , Richard Allaire , Pierre Mongeau The development of spatial competencies through alternating analytic and synthetic activities8 Simon Mochon When can you meaningfully add rates, ratios and fractions?16 Daniel Chazan f(x) = g(x)?: an approach to modelling with algebra22 Peter Bero Calculations in the style of Kepler27 Jeremy Gray , David E. Rowe Felix Klein at Evanston: learning, teaching and doing mathematics in 189331 Heinz Steinbring Problems in the development of mathematical knowledge in the classroom: the case of a calculus lesson37