The pretest-posttest quasi-experimental study examined the effects of small group instruction in number sense on intermediate elementary students. When a student does not have number sense as a strong foundation, it can cause detrimental deficits as the students' mathematical knowledge increases. The gap will continue to grow if effective intervention does not take place. As part of the research in the study, teachers utilized the i-Ready toolbox lessons for a small group intervention to all students within a grade level that score two or more grade levels below on the i-Ready diagnostic assessment in the specific area of numbers and operations. The data were collected over a period of 5 weeks and analyzed from the pre and post data. The effectiveness of the interventions was evaluated based on the comparison of data of overall mathematical achievement and in the area of numbers and operations. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]