At least 500 homes were likely destroyed and there were no known deaths in a wind-fueled wildfire outside Denver, Boulder County Sheriff Joe Pelle said Friday.

Striking teachers picketed outside of schools and marched through Denver’s streets Monday as car horns blared in support of the latest U.S. walkout amid a swell of educator activism in at least a half-dozen states over the last year. Just over half of the 4,725 teachers called in absent for Denver’s first strike in 25 years. Some students crossed picket...