Unit Summary
Please Note: In March 2025, this unit and its lesson plans received a round of revisions. Teachers should pay close attention as they intellectually prepare to account for the updated pacing and content.
This introductory unit focuses on a variety of concepts that students will build throughout the year, including fluently adding and subtracting within 20; counting by ones and tens within 200; and solving add to, take from, and put together/take apart word problems with unknowns in all positions. Students will use appropriate tools, including linking cubes, number bonds, ten frames, tape diagrams, and equations, strategically throughout the unit
MP.5
Use appropriate tools strategically.
and use them to make sense of problems and persevere in solving them
MP.1
Make sense of problems and persevere in solving them.
.
In Grade 1, students added and subtracted fluently within 10 and added and subtracted within 20 using a variety of strategies such as counting on, making ten, going down over ten, using the relationship between addition and subtraction, and creating equivalent but easier or known sums such as using doubles facts (1.OA.C.6). Students also counted by ones within 120 (1.NBT.A.1) and by tens within 100 (1.NBT.B.5). Further, students solved add to, take from, and put together/take apart story problems with unknowns in all positions, though students were not yet expected to be proficient with start unknown problems (1.OA.A.1).
This unit starts off with returning to some of that Grade 1 material in Topic A, namely adding and subtracting within 10 (1.OA.C.6, 2.OA.A.2) as well as counting by ones and tens, though the count sequence is now extended to 200 (2.NBT.A.2). Topic B focuses on adding and subtracting within 20, revisiting all of the strategies seen in Grade 1, such as making ten or using doubles facts, as they now work towards fluency within 20, eventually knowing from memory all sums of two one-digit numbers and related subtractions (2.OA.B.2) by the end of the year. Finally, in Topic C, the focus turns to add to, take from, and put together/take apart story problems within 20, using tape diagrams and equations to represent them (2.OA.A.1). They also pay particular attention to start unknown situations since students are not yet proficient with those subtypes.
This provides an important foundation for work in subsequent units and grades. Students will extend the count sequence to 1000 later in Grade 2, and even add and subtract within 1000 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction (2.NBT.B.7), demonstrating fluency for addition and subtraction within 100 (2.NBT.B.5). These multi-digit computations heavily rely on students knowing from memory all sums of two one-digit numbers and related subtractions, since multi-digit computations can be thought of as a series of single-digit computations, with one for each place in the given numbers. Lastly, students will build on their story problem work by studying compare problems with unknowns in all positions in Unit 3 and then solving two-step word problems later in the year. Beyond Grade 2, they’ll fluently add and subtract within 1000 in Grade 3 (3.NBT.A.2) and study numbers of even greater magnitude (up to 1 million) in Grade 4 (4.NBT.A), where they will also gain fluency with the addition and subtraction algorithm (4.NBT.B.4).