There is a procedural assumption of no design in science. This is because, as you have agreed, there is no physical evidence for design. There never will be any physical evidence for design. There is no way that you can look at a naturally occurring system and provide some OBJECTIVE test that will tell you whether that system is designed or not. (I say objective, as opposed to arguments such as "I can't see how it could have come about without design. Common sense doesn't count in science) Since we can't test for design, design is not a part of science. This is not the same thing as saying that science says that there is definitely no design involved in the development of life. (I grant you that many individual scientists do say this, but this is no more a part of the theory of evolution than inquisitions are a part of Christian doctrine.) Science, in terms simply of the theories that it proposes, pretty much totally ignores the possibility of design, mainly because it has to. This is a limitation of science. I therefore have no problem with teaching the possibility of design. Just don't teach it in science classes, because it isn't science.
Ok.........