This article describes constructivist principles of learning in geometry sp
ecific to children's imaginal anticipations in line measurement and the rel
ated area of fractions. To assist with this discussion, seven sixth-grade s
tudents classified as learning disabled (LD) and receiving some type of spe
cial education service for mathematics were individually tested in tasks th
at investigated their imaginal anticipations of space and their representat
ions of this understanding in the fraction symbol. Additionally, the invest
igation examined the effectiveness of constructivist teaching techniques in
extending student thinking. All students perceived-the most static element
s of the line and could represent a metric unit. In the related area of fra
ctions, they interpreted simple fractions as operational units. However, th
e majority of students were unable to coordinate and, thus, imagine the sec
ond-order nested hierarchies that could be inferred from the line. Similarl
y, they had difficulty coordinating the higher-order nested relationships n
ecessary to interpret equivalent fractions intelligently. The students bene
fited from instruction that questioned their way of knowing and from manipu
latives that served to support their reflections.