Dear Matt, 

I am presuming the chaplain knows you well, so I am going to agree with him. Now, following your vocation will mean taking several steps: it means first of all continuing to develop your prayer-life. You should also have a good long talk with a priest, if you are comfortable with your chaplain and he already knows you to some degree do it with him. What you need to go into with him is your background, your past and present, your family, your spiritual development, your understanding of the priesthood, your motives, your studies, difficulties you anticipate.... Talk about how you are handling your responsibilities now, in the real present. Why? So he can get to know you 'inside out', and so truly help you make a prudent decision and see if this is really for you. Next you need to speak to your parents. You are a sophomore in HS, and so probably underage still. Even if you are not, it is always good to talk these things over with your parents. Some, especially if they feel awkward about the vocation or are really unsure, prefer to leave this until they know a little more clearly, where others precisely value their parents' input even more when things seem murkier. So when and how you approach them depends on how you read the circumstances. You will also need to look into somewhere to go. Have a look into high schools for boys who are interested in the priesthood. If possible visit one or several. See what the life is like, the spirit of the place, chat with the students, see if it would help you. When you come across the place that seems right to you, ask if they will have you. If you are really interested, you might even be able to transfer in at the end of the semester. God bless you in your search.