This is a key debate, which students are expected to be aware of in their Psychology A level exams.
To decide whether Psychology is a Science, we need to establish working definitions of both Psychology and science. If we take Psychology to be the study of the human mind, and accept science to be a process of systematic information-gathering to produce a body of subject matter, then it does indeed seem that Psychology is a science.
Scientific research is based on empirical research, using quantitative research methods such as experiments. Whilst some approaches in Psychology also adopt these methods, there are other approaches that rely on more qualitative forms of investigation such as interview, content analysis and case studies.
Think about the methods used by the different approaches - to what extent is the psychodynamic approach (for example) based on scientific principles?
Some psychologists would go argue that perhaps Psychology is not supposed to be a science; perhaps human behaviour is too complex and unpredictable to measure or generalise in a scientific way. Furthermore, the existence of multiple, competing approaches suggests Psychology cannot be a science because it does not have a single, unified paradigm.
So is Psychology a science? There are no right or wrong answers here except to say that AQA A level Psychology is officially classed as a Science A level...