Mass. Gen. Laws ch. 119 § 21A
Evidence in proceedings under sections 21 to 51H, inclusive, shall be admissible according to the rules of the common law and the General Laws and may include reports to the court by any person who has made an investigation of the facts relating to the welfare of the child and is qualified as an expert according to the rules of the common law or by statute or is an agent of the department or of an approved charitable corporation or agency substantially engaged in the foster care or protection of children. Such person may file with the court in a proceeding under said sections 21 to 51H, inclusive, a full report of all facts obtained as a result of such investigation. The person reporting may be called as a witness by any party for examination as to the statements made in the report. Such examination shall be conducted as though it were on cross-examination. Evidence may include testimony of foster parents or pre-adoptive parents concerning the welfare of a child if such child has been in the care of the foster or pre-adoptive parents for 6 months or more, and may include the testimony of the child if the court determines that the child is competent and willing, after consultation with counsel, if any, to testify.
Mass. Gen. Laws ch. 119, § 21A