Photographers we know: their software includes:
Photoshop 5, 6, 7, CS, CS2, CS3, CS4, CS5, CS6, CC, Elements. Paintshop Pro, Gimp
Xnview, Lightroom, Picasa, Nikon NX, Canon Photo Pro, Aperture, Gthumb, Darktable, RawTherapee, Ufraw, IrfanView, Xnconvert, iPhoto,

There are hundreds of other programmes available.
An image manipulation programme is essential to work with images, but you will usually find other programmes useful to view, edit and batch convert images.

Be open about your attitude to software
Photoshop is not the only programme used by photographers, and for some tasks is not the best.
Whilst the majority of photographers use a version of Photoshop many do not.
Programs for working on images include Photoshop but there are lots of other options.
A newer version of Photoshop will not give you better images.

In addition to an image manipulation programme it is important to have an easy way to view, choose and edit images.
Ideally these programmes will also show RAW files as thumbnails, as well as jpg and tif files.
Proprietary - camera software will show files from one type of camera but where images are obtained from different cameras 'third party' software is a better option. Luckily there are many Open Source pieces of Software available for Linux and to a slightly lesser extent Windows. Mac users have less choice.

The Open Source community can actually provide all software needed to create a Digital Darkroom at no cost.

The Gnu Image Manipulation Programme is more flexible than Photoshop and free to use.

At over £100 per year, Adobe Photoshop is not an easy purchase for a student to make. By only teaching Photoshop you are limiting the possibilities and opportunities of your students, and by inference, virtually encouraging them to pirate software.
Copyright infringement is a criminal offence under the Trade Descriptions Act, the Trademark Act and the Copyright Designs and Patent Act. A successful prosecution could result in a £5,000 fine in a Magistrate Court, or a two-year jail sentence in a Crown Court.

Technique and good file preparation are more important than equipment or software.

Windows, Mac and Linux   

Cost of software for photo-manipulation, DTP, web design and office

Windows and Mac OS
Adobe Creative Suite £548.00 per year.
MS Office £84.00.
Total £632.00 plus £632.00 every year

Linux
Operating system Free
Gimp Free
Gthumb Free
Scribus Free
Libre Office Free
Bluefish Free
Access to thousands of other applications Free
Total cost  £0.00   Saving £1896.00 over 3 years