This smartphone microscope is specifically designed to use in the classroom. With the aid of the threaded rod, you can position the table exactly and adjust the focus precisely. The assembly requires following parts and a bit of soldering (optional).

3 x                Threaded rod length M8 x 120 mm
11 x               Nuts M8
± 25 sq cm         Plexiglas
30 cm              Rubber band (Ninja Flex)
1 x                Lense: 
1 x                Smartphone :-)

I got very good results with these lenses: magnification level round 100x
http://www.aixiz.com/store/product_info.php/cPath/46/products_id/374/osCsid/37cabc139b4f03b0e0a522178defae7e

If you want you can add some LED's so can transform it in a transmitted light microscope. 1 - 3 x LED's 1 x Switch 1 x Resistance (you have to calculate) 1 x 9 V batterie