Getting Started 
Misconception/Error The student does not understand that twodimensional figures can result from slicing threedimensional figures. 
Examples of Student Work at this Level The student does not describe the twodimensional cross section of the prism, but instead:
 Draws a threedimensional piece that results from slicing the prism.
 Draws the net of the threedimensional shape resulting from the slice.
 Draws a two or threedimensional view of one face, showing where the slice will be made.
 Draws the results of a slice other than the one given (e.g., draws a triangle for the diagonal slice).
The student may also confuse some or all of the terms: horizontal, vertical, parallel, perpendicular, and diagonal.

Questions Eliciting Thinking What is the difference between a twodimensional figure and a threedimensional figure? Can you give me an example of each?
Do you know what cross section means? Can you imagine the cross section of the prism that is revealed by the slicing? How would this cross section be different than a net?
Which way is horizontal (vertical)? What does parallel (perpendicular) mean?
Where is the described diagonal? Are there other diagonals? 
Instructional Implications Review the difference between twodimensional and threedimensional figures. Provide the student with examples of figures to be classified as either twodimensional or threedimensional. Ask the student to classify the figures and identify the dimensions of each. Clarify the difference between a â€śnetâ€ť and a â€śsliceâ€ť of the figure, explaining that a section of a net represents a face of the threedimensional figure. Therefore, a net is always congruent to the corresponding faces; however a slice may or may not be congruent to a face.
Consider implementing the CPALMS Lesson Plan Can You Cut It? Slicing ThreeDimensional Figures (ID 47309). This lesson guides the student to sketch and describe a twodimensional figure resulting from the horizontal or vertical slicing of a threedimensional figure. Be sure the student understands the difference between horizontal and vertical, parallel and perpendicular. Model horizontal and vertical slices. Define parallel and perpendicular, and then model parallel and perpendicular slices in relation to the base. Show the student that the dimensions of the slices can be described in terms of the dimensions of the original prism. If needed, provide additional experience with identifying and drawing twodimensional slices of threedimensional figures and describing their dimensions. Consider implementing this task again to assess if the student can sketch and describe the twodimensional cross section resulting from each slice. 
Making Progress 
Misconception/Error The student does not adequately describe the dimensions of the cross section in terms of the dimensions of the original figure. 
Examples of Student Work at this Level The student can identify and draw the shapes of the plane sections, but:
 Does not describe the dimensions at all.
 Describes the dimensions in terms of L, W, and H but does not specify what these variables represent.
 Is not specific in describing the dimensions of the cross sections and only indicates that they â€śdid not change.â€ť
 Incorrectly describes the third crosssection.

Questions Eliciting Thinking You drew a rectangle for each answer. Would each rectangle have the same dimensions?
What do you mean by L, H, and W? Where are these lengths on the original figure?
What are the dimensions of each rectangle compared to the original length, width, and height of the prism?
When you make the diagonal cut, will the length of the cross section be the same as or different from the length of the prism? How will it compare? 
Instructional Implications Guide the student to relate the dimensions of the twodimensional cross sections to the dimensions of the original threedimensional figure. Model a concise comparison (e.g., the height of the rectangular cross section is equal to the width of the prism and its length is equal to the length of the prism). Explain why must be longer than the length of the rectangular prism. Show the student that the length of Â can be described as AH and model using this notation to refer to the length of the cross section in the third problem. Provide additional opportunities for the student to precisely describe cross sections of threedimensional figures.
Consider implementing the MFAS tasks Cylinder Slices, Cone Slices, and Square Pyramid Slices (7.G.1.3) for additional practice. 
Got It 
Misconception/Error The student provides complete and correct responses to all components of the task. 
Examples of Student Work at this Level The student correctly identifies and draws the plane figures resulting from each slice, and describes each using specific dimensions. For example, the student says:
 The cross section is a rectangle with a length equal to the length of the prism and a width equal to the width of the prism (or the same size as side AEHD).
 The cross section is a rectangle with a length equal to the width (or length) of the prism and a width equal to the height of the prism, depending on the direction of the slice (or the same size as side ABCD or CDHG).
 The cross section is a rectangle with a length equal to AH and a width equal to the height of the prism (or forming rectangle AHGB).
Note: The student may label the dimensions of the prism and use the associated dimension labels on the twodimensional shapes, rather than use a word description of the resulting dimensions.

Questions Eliciting Thinking Does the slice have to be in the middle (halfway) in order to be horizontal (vertical)? Can the horizontal slice be close to the bottom (or top) base of the prism?
What happens to the dimensions if the diagonal slice is parallel to diagonal Â rather than through the diagonal ? 
Instructional Implications Challenge the student to:
 Find as many different twodimensional shapes as possible while describing the slice needed to make each one, including slices that are neither parallel nor perpendicular to the base.
 Describe slices from more complex figures such as a double cone or a pentagonal prism.
Consider implementing the MFAS tasks Cylinder Slices, Cone Slices, and Square Pyramid Slices (7.G.1.3) for additional practice.
