Basically this questions kind of bothers me since I graduated. Earlier this year my history teacher said that before WW1 Germany was too weak to be a Great Power but too strong to be considered secondary. Is this true?
No, Germany has unquestionably being a great power since 1871. Prussia before it was unquestionably a great power since 1742. Germany was, by the virtue of her population, industry, a well educated intellectual elite and a strong military tradition, the strongest continental power in Europe by 1914. A subjective ranking of great powers in 1914 across the world would probably place Germany as the third strongest, after the UK and the US.
What was true however is that Germany was not strong enough to be a true global power on the same scale as Britain, nor continental wide power like the US and Russia became. In many ways both WWI and WWII can be seen as an attempt by Germany to transform itself from a mere European continental power to a true global power.