本研究的目的在了解國小二年級學生在數值線段上的數字估計能力，並探討其與數學學習成就的相關性。研究樣本為桃園市某國小二年級學生137人，並以「數字估計任務」及「學齡階段數學能力測驗」收集研究資料，其中數字估計任務分為數字對位置任務（NP task）及位置對數字任務（PN task）。研究結果發現：（1）二年級學生在數值線段上估計0-100的數量表徵已達到線性表徵，且學生在PN task的表現優於在NP task的表現；（2）二年級學生的數字估計能力與數學學習成就具有顯著的相關性；（3）數字估計能力中的NP task表現能預測數學學習成就13%的解釋力，且解釋力達統計意義，顯示NP task表現能有效的預測二年級學生的數學學習成就測驗成績。

The purposes of this study were to investigate second graders’ number-line estimation ability as well as to explore the relationship between their number-line estimation ability and mathematical achievement. The participants in this study were 137 second graders of an elementary school in Taoyuan City, Taiwan, and a number-line estimation task (including number-to-position and position-to-number tasks) and a mathematical achievement test were used as examining tools. The results of this study are as follows. First, on a 0-100 number line, the second graders’ estimates fit the linear model. Significant differences were observed between the number-to-position and position-to-number task results. The students’ estimation ability in the position-to-number task was superior to that in the number-to-position task. Second, significantly positive correlations between number-line estimation ability and mathematical achievement were observed. Finally, the ability to complete a number-to-position task explained 13% of the variance in the students’ mathematical achievement; thus, it can predict students’ mathematical achievement.