Children's use of addition to solve two-digit subtraction problems

Area of Science:

• Cognitive Psychology
• Mathematics Education
• Developmental Psychology

Background:

• Children utilize diverse mental calculation strategies for subtraction problems (M - S = ?).
• The subtraction by addition strategy is one such method, offering an alternative to direct computation.
• Understanding strategy selection is crucial for effective mathematics instruction.

Purpose of the Study:

• To investigate fourth- to sixth-graders' use of the subtraction by addition strategy.
• To analyze how subtrahend magnitude influences strategy choice in subtraction.
• To compare strategy use across different problem presentation formats.

Main Methods:

• Regression models were fitted to reaction times for 32 two-digit subtraction problems.
• Three strategy use patterns were modeled: direct subtraction, subtraction by addition, and strategy switching.
• Performance was compared between subtraction and addition formats.

Main Results:

• Children across grades 4-6 demonstrated strategy switching based on subtrahend characteristics.
• Direct subtraction dominated when the subtrahend was smaller than the difference.
• Subtraction by addition was preferred when the subtrahend exceeded the difference, particularly with large numerical distances.

Conclusions:

• Children's subtraction strategy selection is not random but influenced by problem features.
• The subtrahend's relationship to the difference significantly impacts strategy choice.
• Theoretical models of children's mathematical cognition should incorporate subtrahend properties.