Officials on Thursday indefinitely canceled classes citywide after teachers, striking for a fourth day, blocked streets and swarmed a car attempting to park at an elementary school. Two picketers were slightly hurt as the car rolled through the crowd.

"This behavior compromises the district's goal to ensure that all students will attend safe, orderly and secure schools with climates conducive to learning," said Mary Steele, superintendent of the Gary Community School Corp.

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A substitute teacher arriving for work at Dr. Bernard C. Watson Academy for Boys slightly injured two strikers with her car as she drove through the parking lot entrance blocked by protesting teachers, district spokeswoman Sarita Stevens said.

Police were investigating the incident and no charges had been filed Thursday afternoon.

Union president Sandra Irons called the accidents "unfortunate."

"It's unfortunate that it has gotten to this point," she said.

She said she was unaware of the schools shutdown and had no immediate comment.

Teachers, who began picketing Monday for the start of school, continued to hold signs and march outside the city's 29 schools on Thursday. The have not had a contract since December 2004, and more than 800 teachers and paraprofessionals voted last week to strike. They last staged a strike in 1984.

School officials have offered 2 percent salary increases for 2006 and 2007, while teachers' shares of health insurance premiums would rise from 7 percent to 10 percent.

Irons had said that an agreement still needed to be reached on insurance benefits and the district's efforts to shorten lunch breaks. Talks broke off Wednesday evening.