I'm going to stay a bit longer because I'm taking evening classes to improve my prospects

• If you've decided that further training or a postgraduate degree is the next step for your career development, it is often easier to balance part-time studies with a job you already know well than to start a new job and pursue additional studies at the same time. 
• If your studies relate to your current job, it might be helpful to let your supervisor know. It shows that you're serious about your career.  Perhaps a project you need to do for your course could be tailored to overlap with a project you need to do at work. You may also get financial help from your organisation. 
•  If the course of study you're pursuing is not at all related to your current job, be careful what you say - an employer might think that you have limited loyalty to the organisation.