Bloom's 2 Sigma Problem: A Summary

Bloom's 2 Sigma Problem: A Summary
The trend of one-on-one and private tutoring is significantly growing day by day. However, is this type of tutoring really effective for the better learning of students? Well, Benjamin Bloom gave us the answer to this question long ago!

In 1984, Benjamin Bloom, an educational psychologist, wrote a seminal paper in a journal; The two sigma problem: the search for methods of group instruction as effective as one-on-one tutoring.

In this post, we will go through Bloom’s 2 Sigma Problem in detail, see what it answered, and how it worked. Keep Reading, it will get interesting!

What Is The Bloom’s 2 Sigma Problem?

According to the findings of Bloom’s 2 Sigma Problem, an average student performs two standard deviations better in academics with one-on-one tutoring as compared to the normal learning environment. 2 standard deviations better means roughly converting a C grade to an A; which is incredible!

This phenomenon also describes how factors outside of a teacher's control influence student education outcomes and researches the alternate teaching methods. The whole research was conducted with the help of a tutoring group experiment. However, the whole experiment was reliable enough that its results are still referenced even after 30 years of the research. 

This study claims that almost 80% of the students who were studying in the normal school environment have performed poorly as compared to the ones who took private tutoring. This research paper is shortly known as Bloom’s 2 Sigma Problem. Moreover, since private tutoring is costly and impractical for some people, this paper also discusses ways through which students can achieve similar results. 

The Experiment of Bloom’s 2 Sigma Problem

Now that you know what this research study is about and what were its findings, it is time to go through the detailed experiment used to conduct it. Read on!

Students were randomly added to 3 of these groups:

1. Conventional Learning

In conventional learning, 30 students were assigned to a class with one teacher. There were repeated tests conducted with proper marking. This group of 30 students was basically the control group.

2. Mastery Learning

In mastery learning, 30 students were assigned to one teacher, and the teachers were almost the same as in the conventional class. However, students were given periodic tests for feedback, various corrective procedures, and more repeated tests to confirm if the student has mastered learning the specific subject or concept. The test result of the mastery learning was more than 80%.

3. Tutoring

Only 3 students were assigned to every tutor in this group. These students were also given periodic tests for feedback, corrective procedures, and repeated tests; almost everything same as the master learning. Still, the results of tutoring were better and higher than the mastery learning.

Explained Results

Here are the explained results Bloom got from the groups of mastery learning and tutoring:

Mastery Learning:

In mastery learning, the group of 30 students performed 1 sigma better than the control group of conventional learning. In short, grade B became an A.


In tutoring, the group of 30 students performed 2 sigmas better than the control group of conventional learning. This means that grade C became an A. Also, tutoring worked more efficiently than the mastery learning too, and no need for corrective work was required.

Collectively talking, 70% of the mastery learning students and 90% of the tutoring students reached their desired height of achievement and level of learning. For conventional learning, the result was only 20%.

Why Tutoring And Mastery Learning Effects Were Powerful?

According to Benjamin Bloom, the corrective processes and the constant feedback are responsible for the incredible and positive outcomes of mastery learning. Students did not move on from one topic to another until their concepts are crystal clear. These were the things not present in conventional learning, and that is why the results are poor too.

Tutoring also included all the things that Mastery Learning had. However, did you know what made this group achieve higher results than mastery learning? An undivided, individual, and personal attention by the teachers to the students. 

Other Approaches to Improve Sigma

Though private and one-on-one tutoring is the best way to improve sigma and grades, it is not feasible, affordable, and convenient for everybody. However, Bloom had a solution for this problem too! He researched to find some other ways that could improve the sigma of students. Trust me; these ways are still used and followed by the education industry religiously.
Here are those approaches:

  1. The should be a test set after students finish a course. The test should analyze the understanding level of the students about a certain concept, course, or subject.  This will help to identify their weak points, and what concepts they need to work more on. After identifying, both teachers and students should work on those weak areas. This process is called the corrective process and helps students reach at least the mastery level.
  2. How a student will perform in studies depends a lot on the home environment they are living in. Therefore, teachers should get in touch with parents and ensure students have a safe and supportive home environment where academics are considered important and preferred. However, studies should not be over-prioritized. There should be equal time for leisure activities and studies. Also, parents should provide opportunities for their children to grow. Not only this, but parents should be super supportive and appreciate even the little achievements of their children.
  3. Teachers should work more on the understanding of the concepts instead of rote learning. They need to ensure that the students truly understand the concepts, subjects, and text instead of just memorizing it. Also, teachers should work on the creativity, analytical thinking, applications of principles, and problem-solving skills of their students. 


Now that you have gone through the entire post, we hope you understand what Bloom’s 2 Sigma Problem is, and how it works. One-on-one and private tutoring is indeed an incredible option to enhance and improve the sigma of students. With that being said, at MTS, we have a team of highly qualified and professional tutors to provide you with one-on-one and personalized tutoring for all subjects. With their expertise, our tutors will clear all the concepts and doubts in students’ minds. So, what are you waiting for? Go to our website and hire a private tutor. Your personalized sessions are just a click away!

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With over 3 years of experience in teaching, Chloe is very deeply connected with the topics that talk about the educational and general aspects of a student's life. Her writing has been very helpful for students to gain a better understanding of their academics and personal well-being. I’m also open to any suggestions that you might have! Please reach out to me at chloedaniel402 [at]