Teachers will plan to present the lecture perfectly in a scheduled time; they have the target to complete the syllabus. So mostly they focus on communicating the information they have prepared for their lecture, so they could not find how many of their students understand the class in the way they taught and how many have doubts in the class. So students who have not understand the class and having doubts about some topics could not get answers for their questions. So without finding answers for their doubts, they could not present the right answer in the test, so the wrong answers will reduce their mark. But if they need the answers for their questions and need more marks in the test then they can make use of another way like tuition classes to learn more. The a level biology tutor knows how to teach the students preparing for their entrance test. So based on the requirement the students attend the extra tuition class.
If a person needs to focus extra on the chemistry topic to improve their score then they can search out for the help of the a level chemistry tutor for the guidance. Because if a person has doubts in any subject then the person who is an expert in that subject could help to clear the doubts. Similarly, the tutor knows about the doubts of the students and the technique to clear the doubts flawlessly. While getting the answer for the doubts with the guidance of the tutor the students could learn more new and useful topics.