Time of Frustration

I'm getting to the point of frustration with my Film - Heroes class. I've been trying very hard to be more constructivist - students in charge of discussing different films of their choosing, open dialogue on direction of class, variety of activities to demonstrate student understanding (blogs, reaction papers, option for creative response, discussion), and student choice on other films. However, I feel as though I'm only reaching about 1/3 of the class most of the time. In fact, in my class of 31 (all juniors and seniors), I have 12 students with D's and F's. I love the ideas behind constructivism and student-centered learning, but I fear apathy runs too rampant. Many of these students don't seem to care at all about film - they merely saw the class as an easy grade (but are learning they're wrong) instead of a place to learn. Likewise, I wish I could do without grades, but right now even I feel the grade is the only thing that will motivate some of these low achievers to try harder. My hope is that word will get out that this is NOT a slacker class and the students I do get will be more willing to put in effort and will truly love film. But, at this point, I can only dream of that day.