What do you do when the quiz average is 60%?

My students took a quiz last week and the average score came out to 60%. Students earned scores from 10% to 100% and everything in between. Here's a bit more info:

Number of students who earned 0-19%: 4
Number of students who earned 20-39%: 7
Number of students who earned 40-59%: 7
Number of students who earned 60-79%: 16
Number of students who earned 80-100%: 14

  • 18 students failed and 30 passed (so far)
  • 6 special ed scores are not included because I do not yet have their scores from the special ed teacher
  • 4 students have not taken the quiz due to being absent
  • 23 "accelerated math" students are not included because they follow a different program

The quiz was on perimeter and area with most questions being multi-step problems. For example, one question asked students to find the perimeter of a composite shape made up of a rectangle and a half circle. Of course, students worked through similar questions in class before the quiz. I expected the average to be in the 70s or 80s (as usual).

Thankfully, I'm on vacation this week which gives me time to figure out a plan. How do I organize class time next week to best address this issue? How do I best reteach those who need it and enrich those who did well? When should I give a retake? What would you do?

Help!
Ms. Vila

***Update!*** We spent three more days clarifying the material. Students who earned 80% or above on the initial quiz were given extension activities. Most students took a retake on the fourth day and the average is now in the 80s. Woo hoo!