Shooting Star, an imprint of Enslow Publishers, is looking for shorter fiction and nonfiction books for boys, esp. adventure, mysteries, sports fiction and fantasy fiction.
From their website:
Speeding Star is currently seeking fiction manuscripts and nonfiction queries. We are looking for content written at a 4th grade reading level, but on topics that will appeal to boys and like-minded readers from third grade through high school.
For nonfiction and informational text, please submit a query letter, your résumé, and a sample chapter or other writing sample of your work. Please submit all materials via our submission form.
For works of fiction, we will only consider complete manuscripts between 5,000 and 12,000 words. We are especially looking for adventure stories, mysteries, sports fiction, and fantasy fiction featuring male protagonists but also containing female characters and characters with diverse backgrounds. Your submission must be double-spaced and should also include a résumé or list of works published. Please submit all materials via our submission form.
More information and their submissions form is here.