Q. If I reuse student works from past semesters as examples for future students, does that violate copyright?

For this, it is appropriate to expand to use the term student "intellectual property" (IP) rights rather than simply copyright. If you are instead thinking about student data privacy, instead review WSU's webpage on Student Data Privacy. 

For IP, a starting point is the Board Policy 3.26 Intellectual Property (date of last review: 4/22/2020), which says: 

Intellectual property rights in a student work belong to the student who created the work. A work created by a student to meet course requirements using college or university resources for which the student has paid tuition and fees to access courses/programs or using resources available to the public, is the property of the student. A work created by a student employee during the course and scope of employment is an institutional work and the intellectual property rights belong to the college or university unless an agreement, sponsorship agreement, internship agreement, or other condition described in Subpart B or C provides otherwise.

If you do not gain explicit permission from students to share their work, and the sharing is "unrelated to the evaluation of a student’s academic performance" (see Permission to Use Student Work form), then yes, you may be violating intellectual property policy. To help avoid this and to respect student intellectual property, Minnesota State has a Permission to Use Student Work form on their IP/Copyright Tools and Forms page that is available. Be as clear as you can, and take into consideration whether more than one person was involved in the creation of the work. For example, Board Policy 3.26 also says:

Ownership of jointly created works is determined by separately assessing which of the above categories applies to each creator, respectively. Jointly created works involving the contributions of students and/or student employees must be assessed considering all relevant categories of ownership rights as set forth above.

This is to say: consult and establish written agreements with students and/or other faculty who are jointly contributing to different parts of a work (e.g. recording, video/audio editing, group writing). This includes if you record a student presentation or vice versa, or if there are multiple students working on one work together. For more types of ownership modifications, see the Minnesota State - Student Rights in Intellectual Property page.

To avoid issues late in a course where students may rightfully object to their likeness or works being recorded, copied, or shared, be sure to include information in your syllabus. This gives students time to review their intellectual property rights. 

Removing student identifying information for the purpose of classroom use does not substitute for getting permission. For other uses like accreditation, program review, etc., reach out to Minnesota State professionals who can give more information about whether additional permissions or deidentification practices are needed.

When it comes to intellectual property in these complex educational contexts, the most straightforward way of deciding whether it is permissible to share works is by establishing clear, written agreements around ownership and/or permissions granted.