A concept paper is part of a research project. In this type of paper the student will outline what the topic is that the project is about, why it is worth researching and how the student will preform the research they are writing about. This is a report that precedes carrying out the research or experiment.
A research proposal is similar to a concept paper in that it addresses a specific research project or experiment that you want to complete however it goes into more detail of the research or experiment than the concept paper. In a research proposal you will include literature review in support of the research question and hypothesis as well as a methodology for how the experiment will be carried out. This will include information such as subjects, tools used to collect data, and how data will be analyzed to ensure that the research or experiment is ethical. Unlike a concept paper a research proposal will also be seeking approval from a governing board in order for the student to move forward with the research or experiment.
A research paper is an academic paper in which the student must take a stance on a topic and either analyze information to form a conclusion or take a stance on a topic and make an argument. This type of paper can be a stand alone paper not tied to any other projects or it can occur after research or an experiment has been completed. In the event that it occurs after research or an experiment has been completed the research paper will explain the purpose of the research topic, the process of the research and discuss if the results prove or disprove they hypothesis.