Explain that fractions are parts of one whole. Use the total number of students in the class as the physical model of "one whole." Count with the students to establish how many parts are in this whole. One whole class might contain a total of 24 students. Tell them that 1/24 of the class is one student and that 3/24 is three students. If there is an odd number of students, include yourself, the teacher, in the class count and base the denominator on "total people."
Explore the fraction 1/2 in relation to the number of students. Write the equation "1/2 = ?" on the whiteboard. Ask the class how many students comprise half the class. Elicit ideas for how to find an answer. Some students may say to divide 24 by 2. Others might suggest forming two lines of students side-by-side in pairs and counting how many students are in one line. Try various methods until the class understands that half equals 12 students or "12/24."
Ask what fractional part of the class six students would represent (1/4 = 6/24). Access student thinking again about how to solve the question. Pose the hypothetical question of what the denominator would be if six more students enrolled in the class (30). Ask once again how many students would equal one-half (15/30).
Compare equivalent fractions. On chart paper begin making an equivalent fraction poster based on what students have learned so far. Write "1/2 = 12/24" and "1/2 = 15/30." Ask whether "12/24 = 15/30." Give students time to think, pair up with another student and discuss their answers before asking the class to volunteer answers. Write "1/2 = 12/24 = 15/30" and ask what all three fractions represent (half of a whole group).
Consider other fractional models such as slices of cake. Give each student a pair of scissors and a sheet of copy paper divided equally into 6 "pieces." Demonstrate how to cut their papers in two equal pieces, each representing half the cake. Ask how many slices are in a half (3/6). Instruct them to cut out all 6 pieces, slice each piece in half and determine how many pieces are in half the cake now (6/12).
Conclude the lesson by modeling information that students should record in their math journals including as many equivalencies for 1/2 as they can remember and which parts of a fraction are the numerator and denominator.