The most obvious answer is cost. If a tutor charges the same rate for one or four students, it becomes cheaper per hour as you increase students and share the costs with other families. It is often believed a tutor is best when working 1:1 with a student. In some instances it is well worth the time and money to have 1:1 tutoring and sometimes it is appropriate for students to study and do school work in small groups.
What is not obvious is the dynamics of small group tutoring. In a variety of circumstances it is invaluable for students to learn how to study “what needs to be studied”. The acts of independence and self regulating behavior have far reaching benefits.
Groups need to learn to share and take turns. This seems simple and yet there is the underlying tendency to allow the ‘smart one’ in the group to carry the burden of work. Assuming each student is in the class and has a different point of view/observation about what is happening in class, they should share their observations, pool their resources and determine what indeed is the best answer and supporting information. This requires the confidence of each student in the group as well as all participants feeling comfortable with various ideas and determining the answer collectively. A tutor can help students overcome the foible of ‘one speaking for the group’ by promoting confidence through discussion and also helping students understand what is the kernal or chaff.
In the case of Algebra, if one student knows how to solve an equation, it benefits the student to show another as practice does improve itself to darn near perfection. The other students can benefit from a student point of view explanation and problem solving. A tutor can help limit the instances of misconceptions floating around by correcting processes and adding in details. Sometimes one student may skip a step by being able to factor something more quickly with mental math - a tutor can help all the students in the group learn the math skills for efficient thinking.
There is no one best way to study - there are many ways and usually two or three work well for each subject or manner a class is taught. Being able to select the technique for studying is as important as putting in the effort to study. Tutors, especially those who have been to college and have taught, know many tricks of the trade. Where flashcards may be essential for a small amount of specific facts from the periodic table, discussion and repeating terms out loud may be the success factor for analyzing what happens in a chemistry experiment.
One of the greatest benefits of having a tutor help a group of students learn to study is how this effects each individual when they go to college. College requires both quick uptake and application of vast amounts of information. There is limited time to try out learning to study. Having the ability to create productive study time , work collaboratively with a group (be it lab or a presentation) and select the best process to accomplish the task is one of the large steps to success in college!