I teach part time in a Jewish High School. The following was my response today to a fellow teacher who asked me to recommend a book for teaching Kabbalah to class.
In different years I have used different texts. The common denominator between all the texts that I used was that I was always very familiar with the source material independently from the text's presentation and therefore, able to easily modulate in accordance with the level of the student body. It also allowed me to think outside the text and bring that perspective into the classroom.
For example, this past year we used the anthology called "The Kabbalistic Tradition" by Prof. Unterman. When we read his translations from the Ari z"l on the beginnings of the cosmos, I was able to share with my class ideas culled from the classic commentaries on the original text and also, what some Rabbis who specialize in teaching Kabbalah have orally conveyed to me. So the key might not always be the text itself, as well as how familiar the teacher is with the material to begin with.
Kabbalah is a very vast topic that includes many sub-topics. So you can really work teaching Kabbalah from many angles. Let me suggest two classics that are short and I think if you wanted to you can teach yourself over the span of the Summer. Both are available in English.
The first classic I'd suggest is "Shaar HaYichud V'Emunah", meaning the "Gate of Unity & Faith". It's all about the first verse of Shema and what it means that "G-d is One". I'd suggest skipping the introduction and going right to Chapter One (as the introduction relies on knowledge of a different work by the author). You don't have to buy it. Its available on-line with a linear translation (and commentary worked into the translation). This is what I am strongly considering teaching this year. Here's the link:
The second classic I'd suggest as a possibility is "Tomer Devorah", meaning the "Palm Tree of Deborah". It's short and sweet. It's about how the mystical "Thirteen Attributes of Compassion". The author tells us what these thirteen attributes of compassion look like inside ourselves and urges us to cultivate them and be develop into forgiving people in an act of imitating G-d's ways and drawing down divine forgiveness into the world.
The book is available with a good quality English translation facing the Hebrew text. Here's a link where the book can be bought.
One year I also taught "The Everything About Kabbalah Book". Its also nice. Here's a link.
Another, year I taught Kabbalistic Astrology from Melinda Ribner's "Kabbalah Month by Month. Here's a link if you want to explore it.
I hope I gave you enough material to work with. If you want to discuss anything you can call me at ...