Numbers to 20 on the Number Line

Students locate numbers to 20 on number tracks and lines, reasoning about position relative to 0, 10 and 20 (RTP 1NPV–2 in full): nearer to 10 or 20, halfway, just before and just after — and find one more and one less than any number to 20 by stepping along the line, including across the 10 boundary (one more than 9; one less than 10; one less than 14).