Any time you add an image to your content, you should also include alt text. The alt text is displayed when an image cannot be downloaded due to limited bandwidth and is read to students with visual impairments using screen readers. The alt text should be descriptive, but only include the relevant information a student needs to know.
Charts and other visual data should not rely solely on color to convey information, using text labels and visual patterns to differentiate data points.
All videos and other multimedia (e.g. an interactive activity), should include captions or a transcript. Captions can easily be added to videos by using YouTube. Videos uploaded to YouTube are automatically transcribed; automatic captions can be edited by the owner of the video. (In fact, don't rely on auto-captioning, there are likely errors you'll need to fix, but it's a good headstart and provides an option for your students if nothing else is available.) Captions help both students with hearing impairments and students with learning disabilities. Captions also enable students to watch videos without audio when necessary.
Videos should be stored online using YouTube or Google Drive (which also allows for caption file uploads), to ensure the video will play on all devices. These services automatically convert and resize videos depending on the user's device and network capabilities.
In Practice:
All video must have time-synchronized captioning that is either enabled by default or easily turned on. It should have good background-foreground contrast and be properly "chunked" for easy reading. The video below provides information about captioning in YouTube.
YouTube offers a number of captioning options. You can transcribe the videos yourself and edit timestamps; you can let YouTube transcribe your video automatically and then you can fix up any errors that occur and you can upload (or allow others to upload) files that will caption your videos. Additionally, other providers offer a variety of tools to help individuals caption YouTube or other videos. For instance, Rev.com will caption your videos for $1 per minute and send you back the caption file within the next day. That can be well worth the money for the time it will save you.
It may also be that your district has the staff who know how to edit SRT or TXT files that can be uploaded as captions. If you are in Intermediate District 287 you can reach out to the Teaching & Learning Department to discuss the best options.
The education market moves quickly and evaluating tools and resources can be a challenging task. The W3C Web Accessibility Initiative provides a great variety of resources including a W3C Cheat Sheet that provides a quick guide to accessibility.
This page by Jon Fila and Caitlin Cahill at Intermediate District 287 is licensed CC-BY-NC-SA. Based on a work from Leading Edge partners: @One, iNACOL