*TERC Investigations* is the core mathematics curriculum for 4th grade. The goal is to help all children understand the fundamental ideas of number and operations, geometry, data, measurement and early algebra through hands-on and collaborative investigations. Proficiency with arithmetic skills is supported throughout the program. A variety of assessment techniques including observations, students' self-assessments, quizzes, homework and individual oral assessment are used. Extensions or review sessions are offered to accommodate students who need further challenges or additional help.

The principal concepts taught in Fourth Grade are:

- An understanding of, and the ability to use various algorithms for the addition and subtraction of multi-digit numbers;
- Mastery of multiplication facts through twelve and multiplying by two and three digits;
- Division with remainders is introduced and mastered;
- Order fractions, finding equivalent fractions, adding and subtracting fractions with common denominators;
- Identification on a number line the relative position of positive fractions, positive mixed numbers, and positive decimals to two decimal places;
- Recognition that rectangles that have the same area can have different perimeters;
- Knowledge of the definitions of a right angle, an acute angle, and an obtuse angle. Understand that 90°, 180°, 270°, and 360° are associated, respectively, with 1/4, 1/2, 3/4, and full turns;
- Knowledge of the definition of different quadrilaterals (e.g., rhombus, square, rectangle, parallelogram, trapezoid);
- Analyze problems by identifying relationships, distinguishing relevant from irrelevant information, sequencing and prioritizing information, and observing patterns;
- Express the solution clearly and logically by using the appropriate mathematical notation and terms and clear language; support solutions with evidence in both verbal and symbolic work;
- Estimation, mental arithmetic and problem solving strategies are also reviewed and practiced.