For educational videos, sites such as TeacherTube ,SchoolTube ,and safeshare.tv offer alternatives to YouTube. These sites are often unblocked by school networks, as the content is monitored and is all educational. If your teachers use any alternative services, use those to reduce the risk of being caught on web monitoring services. Use one with an SSL certificate. To tell if a website has an SSL certificate, its URL should say https rather than http, or there is a green padlock icon next to the URL. This allows encryption to prevent being caught if the internet you are using is monitored. Look for the video hosted on a site other than YouTube. There's a chance that this site will not be blocked by the network. Be careful when visiting unknown sites, as some contain viruses and other malware.

Summary:
Find an alternate portal. Search for your video using a search engine.