The Montessori Constructive Triangles

I am so excited to introduce to you the Montessori Constructive Triangles!  This is one of my favourite Montessori material because I find it useful  for my 3 years old and my elementary.  In this post, I’m showing you each of the content of the boxes and how it is being used in learning plane geometric shapes.


What is Montessori Constructive Triangles?
Montessori Constructive Triangles are both sensorial (3-6) and geometry (6-12) Montessori materials.  It usually consists of a set of 5-6 boxes which contain different types of triangles used to form rectilinear or right angled figures.  It is called “constructive” because it introduces the child to the concept of visual images that may be combined to form different shapes.

For what age?
The materials are introduced around 3 years old as sensorial materials.

Box 1:  Rectangular Box


This is the first box that is introduced to the child.  It contains the following:

• 2 small equilateral triangles with black lines along one of the edge
• 2 right-angle isosceles triangles with black lines along the hypotenuse
• 2 yellow right-angle isosceles triangles with black line along one of the sides
• 2 green right-angle triangles with black lines along the longer right angle sides
• 2 yellow right-angle scalene triangles with black line along the shorter of the two right angle sides
• 2 grey right-angle scalene triangles with black line along the hypotenuse
• 1 red right-angle scalene triangle and 1 red obtuse angle scalene triangle

The black line is used as guide in forming the shapes.

Box 2:  Blue Triangles / Second Rectangular Box


The second box contains blue triangles without black lines.  Here the child can freely form his shape without using the black line as a guide.

• 2 blue right-angle scalene triangles
• 2 blue right-angle isosceles triangles
• 2 blue equilateral triangles
• a pair of smaller blue triangles identical to the shape and size of the red triangles in Box 1

Box 3:  Triangular Box


This box contains the following:

• 3 yellow isosceles obtuse triangles with black lines along both sides of the obtuse angle
• 4 red equilateral triangles, one with black lines on all sides, three with black lines one one side
• 2 green scalene right triangles with black lines along the longer of the two sides of the right angle
• 1 large grey equilateral triangle without black lines

Box 4:  Small Hexagonal Box


The hexagonal boxes are my personal favourites.  There’s just so many things you can do with them, especially when making equivalence (more of this in the elementary post).  Anyway, here are the contents of the the small hexagonal box:

• 6 red obtuse-isosceles triangles with black lines on the side opposite the obtuse angle
• 1 large yellow equilateral triangle with no black lines
• 2 red equilateral triangles with black lines on one side
• 3 green equilateral triangles, 2 of which has black lines on one side, and 1 with black lines on two sides
• 6 grey equilateral triangles with black lines on two sides

Box 5:  Large Hexagonal Box


The large hexagonal box contains a different set of triangles compared to the small hexagonal box.  Here are the contents:

• 1 large yellow equilateral triangle with black lines on all three sides
• 3 yellow isosceles obtuse triangle with 3 black lines on the side opposite the obtuse angle
• 3 yellow isosceles triangles with 3 black lines on both equal sides
• 2 red isosceles obtuse triangles with black lines on the side opposite the obtuse angle
• 2 grey isosceles obtuse triangles with black lines on one of the sides of the obtuse angle

Box 6: Blue Triangles

Most Montessori Constructive Triangles set doesn’t come with this, and it is sold separately.  In my case, this was part of the set I bought so I will just have to introduce this as well.


This box comes with 12 right angle blue triangles with no black lines.  The child is encouraged to freely create patterns using these triangles like the pinwheel below.  The child can create as many designs as he can come up with.  For guides, you can check some triangular patterns from Montessori Print Shop.


How to Use for 3-6 Year Olds

To introduce each box, remove the triangles and place them (in pairs if possible) into the rug/table close together but not touching with their black line edges.  Start with one pair, say the grey triangles.  Hold one triangle with one hand and run your index finger of your other hand along the black line.  Do this to the other triangle and gently push the two grey triangles together so that their edges with the black lines are touching and coinciding.


Do this with the rest of the pairs of triangles in the box you are presenting.  I named the shapes we formed because Vito is familiar with some of them.


Mavi, my 9 years old, is using this in a different way.  I will dedicate a separate post on how older kids can use these Constructive Triangles in basic Geometry.

Stay tuned for more how to’s on Montessori and Montessori inspired activities!