Depending on the curriculum being used, a child can be introduced to rays in 3rd or 4th grade. A ray is taught in conjunction with its cohorts: points, lines, segments and angles. It is an easy and fun concept to teach if you use the ideas given here.
A line goes in two directions to infinity. A line segment is a portion of a line that has a definite beginning and ending, often demonstrated with a point - or dot - at each end or as a segment of a line. A ray starts at a point and goes forever in one direction. Angles are two rays that start from a single point.
Demonstrate rays and their cohorts using your arms. Raise both arms straight out to the side and point with your fingers to demonstrate a line. You may tell the students that you can never truly make draw a 'whole line' because it goes on forever and ever, so that's why you draw arrows when making a line on paper. Keep making the line, but close your fists to demonstrate a line segment with definite points where it begins and ends.
Raise one arm in any direction and point to demonstrate a ray. Use both arms as rays to demonstrate angles. Draw the figures on the board with arrows at the end of a line to show it going on and on, two dots (labeled A and B) on the line to show the line segment and a dot and arrow at the ends for rays.
Have the kids practice making these objects by playing a game of 'Simon Says.' Alternatively, art activities include pasting toothpicks to construction paper, drawing arrows at the ends as appropriate and labeling each figure. Or you can use frosting instead of paste, pretzels instead of toothpicks and freezer paper instead of construction paper. Then, the kids can eat the results after they have been checked for accuracy.
Read and show a colorful book about rays and related objects. One example is Lines, Segments, Rays, and Angles by Claire Piddock.
There are several songs that reinforce geometry terms, like rays.
Point, Line Segment, Ray, on Barbara Speicher's album Learning Math by Song. This song also has movements using body language similar to that discussed earlier.
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